There is behavioral evidence that fetal rats can detect and learn about their amniotic milieu. Recent physiological evidence has now implicated the accessory olfactory pathway as one neural substrate for processing odorous substances prenatally. However, virtually nothing is known about the functional role of this pathway for developing animals. The goal of this proposal is to characterize the anatomical and functional development of the accessory olfactory pathway. This will be done by using neuro-anatomical/physiological techniques that have been successfully applied to the developing olfactory system. Horseradish peroxidase tract-tracing experiments will document the timing of peripheral connections in the accessory olfactory pathway as well as their topographical arrangement. 2-deoxyglucose experiments will establish the age of onset of functional activity in this pathway and the conditions that contribute to this activity. Cytochrome oxidase experiments will substantiate and extend the prevous studies by detailing the ontogenetic pattern of functional activity in this pathway. Together, these experiments will provide a coherent foundation for assessing the functional significance of this pathway during development. Since this may be the first functioning olfactory system in the developing rodent, these findings will be significant for establishing early sensory function in the fetus and neonate. This will not only provide insight into olfactory processes but enhance our understanding of developmental processes of brain maturation in general.